This concerns my 96 XJ, 4.0, etc. Over the course of the last 4-5 weeks I have replaced the power steering pump, radiator (alum, 3 panel), radiator hoses, flushed the heater core and changed the serpentine belt (a gator back). I have not changed the water pump nor the thermostat .... yet. Well, since changing the radiator etc, I am modestly concerned because the temp never reaches above 155 degrees now. I drove about 20 miles today with the AC on and the outside temp was about 70. Prior to making the above changes the temp gauge almost always was running at 210 or slightly above. Is it normal for that much of a decrease and for it to never reach above 155 after what has been changed ? I'll probably buy a radiator cap with a temp gauge embedded just for an alternate reading. Should I be concerned about the temp sending unit or just consider myself lucky?

 

Hit it with an infrared thermometer and see what the actual temp @ the thermostat housing is. If you could get an XJ to run 155 deg merely by changing the radiator, half the posts here wouldn't exist. More likely an issue with the gauge/sender.

 

Yea, I kind of figured all the planets didn't just align correctly and BAM I have the coolest running XJ ever ;-) .Guess I'll stop by Home Depot today and pick up a infrared thermometer.

 

Or do it right, and spend 50$ for a water pump, and 20$ for a thermostat and sending unit and know for certain that you eliminated that problem. An IR thermometer will run you 40 -60$ to only tell you that either needs to be replaced, then you are out double the cost of the origional replacement. Its pretty typical that aging XJ's need a new waterpump and thermostat.

 

Sounds like the t-stat is busted. Waterpump and T-stat are longterm maintenance items.

 

Both the water pump and T stat are on my list. I'll probably go ahead and purchase a hi-flow pump, t-housing and a 190 t-stat. Any reason not to go with those over the stock units? Or are the hi-flow units just a waste of $$ for a basicly stock XJ

 

waste of money. A stock system will maintain temps just fine when in proper working order. Unless you want to get the hi flow pump, but i see no reason to. Thermostats are designed to fail open, so in the event of a failure you wont overheat. Its possible a chunk of crud got in to the spring seat and is keeping it from closing.

 

Q: Any reason TO go with those over the stock units?

A: No.


Sitting at 155 is not the result of a t-stat that's stuck open. Take the t-stat out completely and it will still heat up to normal operating temperature eventually. It will just take longer. If it's staying at 155 and you've been driving a half hour or more, it's probably not an accurate temperature reading.

You need to get a temperature measurement independently of the stock gauge. Rent an IR unit or something.

 

You get your money out of them pretty quickly. I've used them to find noisy accessory pulleys, failing u-joints, failing wheel bearings, transmission cooler blockages, bad electrical connections, checked the wife's oven thermostat.... it's a handy tool.

 

Don't depend on that for anything. I've seen as many fail closed as open.

 

Being an old grunt, I will just go with the shotgun methodology. Replace it all and let others sort it out ;-). I've purchased a new water pump, 195 degree thermostat, and new gasket. I'll have to track down a new sensor/sending unit since my local NAPA was out of stock. I'll still go ahead and get an infrared thermometer today and trouble shoot it to track down the actual fault. If the sending unit is still good, than I will have a spare if I should need one for one of my other XJs. Guess I'll just have to postpone redoing the headliner I took out last weekend to fix this first. It's not a DD so now worries.

 

My buddy bought an xterra that never raised off the L mark on the temp gauge, never blew warm heat out the vents and had radiator hoses cold to the touch even after 50 mile highways trips. Took the thermostat housing off (PIA have to take the entire front end off along with the timing chain cover just to get to those 3 tiny 10mm bolts) and found there was no thermostat in. Replaced and now it heats up and stays at normal operating temperature and blows hot air out the vents even on cold winter days.

 

Dealer or play "whatever third world country made them this week and threw them on the boat".

 

Yep. Stick with dealer stock on sensors for these beasts.

 

If the cooling system has a lot of excess capacity that can happen. The XJ doesn't fall into that category.